Donald Trump and his supermodel girlfriend – who boasted over the radio that she was naked – told the world all about their “exceptional” sex life yesterday, hours before Trump released a strip-the-rich tax plan.

Trump, who’s talked about running for president as a Reform Party candidate, told shock jock Howard Stern in a sex-drenched phone interview that gorgeous Melania Knauss could become Wife No.3 – “a potential first lady,” he said – and that he often “mentally” feels her up in public.

Knauss, who claimed she was sitting nude next to her developer-boyfriend in his Trump Tower penthouse – said she and Donald have incredible sex at least once a day and sometimes “even more.”

“We have a great time,” the Austrian beauty cooed to Stern.

“When we walk into a restaurant, I watch grown men weep,” Trump said, bragging about how his conquests enhance his stature.

Stern asked Trump what was a bigger thrill – having sex with the Austrian-born Knauss or watching her lie out in the sun with nothing but a thong bikini.

“I think all of the above,” the builder laughed.

Russ Verney, the chairman of the Reform Party and a longtime ally of party founder Ross Perot, was not laughing when he heard about Trump’s racy interview.

“I’d be shocked,” Verney said. “The very first principle of the Reform Party is to set the highest ethical standards for the White House and Congress, not the most base, crass attempt to appeal to the lowest common denominator.

“Whatever their private life is, it should be exactly that – their private life.”

But Trump, who has poor support in the latest polls, said that if President Clinton were caught with a supermodel – instead of plump-but-now-slimming ex-intern Monica Lewinsky – “he would have been everybody’s hero.”

After his turn with Stern, Trump released a plan to hit the rich with a 14.25 percent surtax on every person and trust valued over $10 million – with the goal being to erase the national debt.

“It’s a big hit for me, but I think it’s worth it,” Trump said, claiming his net worth is $5 billion which, if true, would mean his own tax hike would cost him $725 million.

Trump’s political adviser, Roger Stone, said it’s unlikely Trump would release his tax returns – as many presidential candidates do in the spirit of full disclosure – to verify Trump’s worth.

Reform Party opponent Pat Buchanan, campaigning upstate, called Trump’s plan a “foolish idea” but said he’d like to see Trump make a “lead-off voluntary contribution.”